Frequency stabilization system



June 29, 1948 H. E. GOLDSTINE 2,444,194

FREQUENCY STABILIZATIONSYSTEM Filed March 20, 1944 -3400l ozrs.

INVENTOR ATTORNEY Patented June 29, 1948 FRE UENCY STABILIZATION SYSTEM Hallan E. Goldstine, Port Jefferson, N. Y., as-' signor to Radio Corporation of America, a corporation of Delaware Application March; 20, 1944, Serial No. 527,189

2 Claims. 1

This invention comprises a frequency stabilized inductive output electron discharge device circuit.

Inductive output electron discharge device circuits are known in the art. One such circuit, given by way of example only, is described in an article entitled A wide band inductive output amplifier, published in the Proceedings of the I. R. '13., March, 1940, by A. V. Haefiand L. S. Nergaard. Such a circuit includes a cavity resonator having a gap and an electron discharge device for propagating a modulated or interrupted stream of electrons across the gap of the cavity resonator. The passage of the electrons across the gap induces energy in the cavity resonator.

One difliculty heretofore experiencedin these inductive output systems has been the reduction 1 in the Q of the system due to the loading on the cavity resonator caused by losses in the electron tube, losses in the glass envelope of the tube, and the loading caused by the power taken from the cavity resonator for utilization purposes. The in ductive output system is also somewhat aifected by heat from the electron tube, which may also cause the electron stream to depart somewhat from the desired normal path. The heating of the electron tube due to its operation over a period of time often causes the dimensions of the tube elements, including the glass envelope, to change. These changes are reflected in the resonant frequency of the cavity resonator.

The present invention has forits primary object to overcome the foregoing difiiculties by stabilizing the frequency of the inductive output system to a high degree, and this isaccomplish-ed by the use of a frequency stabilizing elementso coupled between the input and output of the systern that the frequency of operation is dependent substantially solely upon the characteristics of the frequency controlling element. In the preferred embodiment of the invention, this frequency controlling element is a highly stable, temperature-controlled concentric line resonator of high Q which is coupled between the output of the cavity resonator and'the input of the electron discharge device through short coupling lines of relatively low Q. By suitable adjustments, the circulating energy in the concentric line resonator employed as the frequency deterthe fact that the coupling lines between the inductive output syste'mand the frequency controlling resonator have reasonably broad frequency characteristics, it will beevident that the high Q concentric line resonator is the predominant frequency controlling-element. r

A more detailed description of the invention follows in conjunction with a drawing, whose single figure illustrates the preferred embodiment of the present invention.

Referring to the drawing in more detail, ther is shown an electron discharge device I, comprising avacuum tube structure consisting of an evacuated glass envelope 2 containing therein a cathode 3, heater 4 .amodulating grid 5, ringlike accelerator electrodes 6, and a collector electrode 1, the lattercontaining therein a suitable suppressor electrode 8 This type of electron discharge device is now well known in theart and is not being claimed per se, the showing being given merely to illustrate how it fits into the cavity resonator l2- and associated apparatus. By

wayof example only, this vacuum tube may be an RCA 825 type inductive output tube.

Surrounding the exterior of the electron discharge device I in symmetrical fashion, and located intermediate the tube accelerator electrodes 6, there is provided the high Q low loss tank circuit 12 in the form of a cavity resonator consituted by a copper cylinder ['3 whose ends are closed by truncated cones made of sheet copper l4 and 15. The dimension of the cavity resonator i2 as measured from the center of the glassenvelope 2 toward the arc of a sector shown in dotted lines at H is approximately"one-quarter of the lengthof the communication wavecorrespending to the resonate frequency. It should benoted that the shape of theresonator [2 de'-- parts somewhat from: that shown in such copending applications as serial Nos-. 296,045 and 346,106, respectively filed September 22, 1939, by Fred H. Krogeigand July 18, 1940, and now U. S. Patents 2,350,907 and 2,373,233 granted June 6, 1944and April 10, 1945 respectively, by Orville E. Dow, mainly in the lengthening: of the cavity resonator at the extreme edges and in the shortening of the cavity resonator at the center, dueto the provision of the cylindrical element 13. In effect, this type of cavity resonator can be referred to as an hourglass or re-entrantcone type of resonator. The cavity resonator is provided with a gap at 5 across which the electron stream in the device 1 passes. In order to vary the resonant-- frequency of the cavityresonator 12 to alimited' degree, the gap at Bis-made adjustable, one sidev of which is formed by a copper plated iron sleeve '0, the other side of which is formed by an iron sleeve piece I I, as a consequence of which there is obtained a, variation of the capacity between the sides of the gap. Sleeve I is made to move in l4 and [0.

For focussing the electron beam,,there is provided a pair of magnetic lenses in series relation, constituted by gaps 9 and I6 formed by spaced iron sleeves l8, l0 and II which surround the glass envelope 2 and are serially arranged with respect to an iron magnetic path. .This magnetic path includes a strip of iron H! which is placed adjacent to the sides of the upper sector of the tank l2 and which is completed through an iron core 20; in turn surrounded by an electromagnetic field coil or solenoid 2| excited by a direct current source of supply 22. If desired, the magnetic path may be supplied by a permanent magnet which would then replace the field coil 2! and the yoke 20.

The cavity resonator I2 is maintained at ground potential, while the cathode is maintained at a potential of about 3400 volts negative with respect to ground, thusmaintaining the cavity resonator at a potential which is relatively positive with respect to the cathode. The accelerat-or electrodes 6 are also connected'to ground through suitable resistors, as shown, and hence are also at a relatively high positive potential relative to the cathode. The collector electrode 1 is maintained at 2000 volts relative to ground and thus held at a high but lower positive'potential than the accelerator electrodes relative to the cathode. The suppressor electrode 8 is connect- 'ed to a point on a potentiometer connectedbetween 2000 volts and 3400 volts and is thus at a somewhat higher positive potential than the collector electrode relative to the cathode. The potentiometer is adjusted to supply the suppressor with the proper voltage to reduce current to a minimum in the adjacent accelerator electrode,

7 such as might be due to secondary emission from the collector. t

In order to stabilize the frequency of the system, there is provided a high Q concentric line resonator 25 having an inner conductor 26 provided at one end with aSylphon bellows 21. The overall length of the inner conductor 26 is maintained constant despite fluctuations in tempera- .ture, by virtue of the Sylphon bellows 21 which isconnected to one end of the concentric line resonator by means of the Invar rod 28 of low temperature coefiicient characteristic material. By means of suitable elements (not shown), this concentric line resonator is of the type described in Kroger United States Patent 2,108,895, granted Feb. 22, 1938. In practice, the Invar rod 28 passes through one end of the cavity resonator and is fastened to a suitable platform 29 of se-' lected materials for enabling either positive or negative temperature correction, as desired.

The concentric line resonator 25 is coupled to the output of the inductive output system by means of a short length of transmission line 30. Line 30 is coupled at one end to the interior of the concentric line resonator 25 by means of an adjustable loop 3|, and is coupled to the interior of the cavity resonator 12 at its other endby means of the adjustable loop 32. .Loops 3| and 32 are rotatable in position in order to vary the degree of coupling. At the end of line 30 adjacent the cavity rescnator l2 there is provided a circuit comprising a coaxial line stub 33 whose effective length is adjustable by means of a slider 34 which short-circuits and is movable over the lengths of inner and outer conductors of stub 33. A variable condenser 35 is'provided between the cylinder I3 of the cavity resonator l2 and that end of the loop 32 which is directly connected to the line 30. Stub 33 is in effect a tuning inductance and this element, in combination with the condenser 35, provides a means for tuning loop 32. The impedance of the line 30 may also be matched to that of the loop 32 by means of suitable adjustments of the line stub 33 and the condenser 35. For a more detailed description of a coupling system for use between a cavity resonator and a utilization circuit, employing a coaxial line stub and a tuning condenser across the coupling line, reference is made to copending application Serial No. 346,106, filed by me and Orville E. Dow on July 18, 1940, now United States Patent 2,373,233, granted April 10, 1945.

The concentric'line resonator 25 is also coupled to the input or grid circuit of the electron dis-charge device I by means of a coaxial transmission line 36. One end of line 36 iscoupled to the interior of the concentric line resonator 25 by means of an adjustable loop 3'! which is rotat-. able in the interior of the concentric line resonator in order to vary the degree of coupling thereto. The coaxial line 36 is inductively coupled at its other end to the input or grid circuit consisting of loop 38 and variable condenser'39. The grid is connected to the loop 38 by means of an adjustable tap. Condenser 39 at one end of p 38 serves to tune the grid circuit. Condenser 40 at the other end of loop 38 serves'as a by-pass condenser.

Coaxial lines 30 and 3B are made as short as is feasible and are arranged and operated so as to have reasonably broad frequency characteristics; hence, these coaxial lines have much lower Qs than either the cavity resonator l2 or the concentric line resonator 25. The concentric line resonator 25,. on the other hand, is a very high Q, circuit which has a sharp frequency characteristic, and for this reason this concentric line reso nator is of primary importance in controlling the frequency of the system. The feed back path including coaxial line 30, concentric line resonator 25, coaxial line 36 and the associated loops and adjusting elements are so adjusted that the phase of the feedback is suitable for producin stable oscillating conditions. In practice, the cavity resonator l2 may-develop as much as twenty watts in its interior, of which only a relatively small amount (such' as, let us say, of the order of one watt) is necessary to drive the grid circuit. Another relatively small amount of power of the order of one watt may be-used to drive a suitable utilization circuit, such as a power amplifier in put circuit which is shown coupled to the interior of cavity resonator I2by means of adjustable loop 4|. cavity resonator [2 may circulate in the concentrio line resonator 25. Thus, by way of example, there may be about 18 watts lost circulating in the concentric line resonator 25, whereas only one watt of this is used to drive the grid through the coaxial line-36. It-will thus be seen'that the ratio of the power in the concentric line resonator to the power usedto drive the grid circuit is relatively high. These factors all enter into pro- The remainder of the power developed in the ducing a highly stable frequency of operation. It is preferred, though not essential, that the impedance of the transmission lines 30 and 36 be approximately matched to the impedances of the circuits at their output terminals so as to minimiZe standing waves in the lines.

In one embodiment of the type illustrated in the drawing and successfully tried out in practice,

there was obtained a high order of frequency stability of the order of two parts per million per degree centigrade, with the transmitter operating on 474 megacycles.

What is claimed is:

1. A frequency stabilized inductive output system comprising a temperature controlled concentric line resonator of high Q having distributed constants, and individual coupling circuits between the output and the input of the inductive output system and said high Q concentric line resonator, said coupling circuits having relatively broad frequency characteristics and having an appreciably lower Q than the Q of said resonator, whereby said concentric line resonator is the predominant frequency controlling element for said system, said coupling circuits comprising short sections of coaxial transmission lines, the coaxial line coupling the output of the inductive system to said high Q concentric line resonator having adjustable loops at both ends for varying the degree of coupling and also having a tuning stub connected thereto, the coaxial line couplin the input circuit of the inductive output system to the high Q concentric line resonator having an adjustable loop at its input terminal located in the interior of said high Q resonator, the output end of said last line being inductively coupled to said input circuit.

2. An inductive output system having a cavity resonator in the form of a surface of revolution and having a gap across which a stream of electrons may pass, a grid electrode on one side of said gap for modulating the intensity of said stream, and a collector electrode on the other side of said gap, a frequency stabilizing circuit comprising a temperature-controlled concentric line resonator of high Q, and individual coupling circuits connected between the output of said cavity resonator and said grid and said concentric line resonator, said coupling circuits comprising short sections of coaxial lines having appreciably lower Qs than the Q of said concentric line resonator, said coaxial lines having relatively broad frequency characteristics, the coaxial line coupling the output of the cavity resonator to said con centric line resonator having adjustable loops at both ends for varying the degree of coupling and also having a tuning stub connected therewith, the coaxial line coupling said grid to said concentric line resonator having an adjustable loop in circuit with one end and which loop is located in the interior of said concentric line resonator.

HALLAN E. GOLDSTINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,109,880 Dow Mar. 1, 1938 2,232,179 King Feb. 18, 1941 2,280,824 Hansen et a1 Apr. 28, 1942 2,311,520 Cliflord Feb, 16, 1943 

